File Renamer Lite is a great batch tool for file renaming. The Lite version is the cheaper version of File Renamer, which sells for $19.95. It is almost identical, but it has the limitation that you can only process 50 files at once. The limit is not 50 files overall, just at once. With this tool, you can rename your files in many ways.
There are quite a few different renaming modes: numerical and alphabetical sequence renaming, insert/delete, replace/remove, date and time, general, MP3/AAC renaming using ID3 tags, photo renaming using metadata, among others.
I tested the app with the ID3 tag renaming mode. Basically, what this mode does is read the ID3 tags of your MP3, AAC, M4A and M4B files and replace the current name of your files with a combination of fields from the tags. For example, if your mp3 song looks like this: "I gotta feeling.mp3", you can rename that using this tag order: Year - Artist - Title, which will make your file look like: 2011 - Black Eyed Peas - I Gotta Feeling.mp3. You can even set any separator you want. And this is all done automatically. But your songs need to have ID3 tags for this to work.
All in all, despite the 50-file limitation, File Renamer Lite works very well. If you need to process more than 50 files at a time, you can buy the full version.